Since HVAC systems involve plenty of moving components, it is normal to have some vibration and noise, even in a correctly installed and well-maintained system. However, excessive vibration and noise indicate that an installation should be serviced, and they can also lead to other performance issues.
Vibration and noise are normally addressed together because they are closely related; the second is often a consequence of the first. Some property owners only focus on noise and use plenty of soundproofing, but this is not the best approach because it does not solve the underlying issue.
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Common Sources of Vibration
In HVAC installations, vibration often originates from rotating machinery or from bulk air movements. Vibration tends to increase with time as system components wear down, but it can also be present in new installations as a consequence of poor design decisions:
- Excessive vibration can be caused by an oversized compressor or chiller. This also leads to extra capital expenditures, additional power requirements, and a shorter equipment service life - oversized units cycle on and off more frequently.
- Oversized fans and blowers can also cause excessive vibration.
- In HVAC systems that use hydronic piping, water pumps can also be a source of vibration. Like with compressors and chillers, the effect can be minimized with adequate equipment selection and the use of damping pads.
- Even if equipment is properly sized, vibration issues can arise from the use of inadequate supports. There are neoprene and fiberglass pads that minimize the vibration transmitted between moving equipment and the underlying structure.
- Poorly designed air ducts can suffer from high pressure or airspeed, and this can also be a source of vibration.
- In general, any piece of equipment that rotates can produce vibration if the shaft is not aligned properly. Special attention should be given to shaft couplings between different pieces of equipment, for example between an electric motor and a centrifugal pump. The centerlines of both shafts should match as closely as possible to minimize vibration.
Vibration can only be felt directly in some cases - humans are more likely to perceive vibration when frequency is low and magnitude is high. However, negative consequences start before this point is reached: many mechanical components are very susceptible to vibration, especially the bearings on rotating machinery.
The best way to control vibration is to prevent it with smart design choices. In existing installations, it can be minimized with adequate maintenance and by installing damping pads or spring mounts for rotating machinery. Keep in mind that eliminating vibration completely is not possible, but it can be reduced and isolated to a point where its effects are negligible.
In general, excessive vibration increases the ownership cost of building systems. Maintenance expenses and downtime tend to increase, and the associated noise can be distracting in work environments. In the industrial sector, uncontrolled vibration can lead to product quality issues. For example, propagated vibration can affect the performance of machining equipment, leading to incorrect product dimensions and other similar defects.
Propagated Vibrations and Noise
When troubleshooting vibration, keep in mind that it can propagate. In many cases, most of the noise is produced by building components that are affected by propagated vibration from other sources. Dropped ceiling grids can become very noisy when subject to vibration, since they have plenty of contact points with ceiling tiles and luminaires.
In new constructions, a good recommendation is to define a building layout where occupied areas are not adjacent to mechanical rooms or other sources of noise and vibration. This provides comfort for occupants, while reducing the need for soundproofing between different building areas.
Addressing Noise from Aerodynamic Effects
Excessive wind speed and turbulence can also cause noise, and direct exposure to air drafts is uncomfortable and detrimental for health. These effects can be minimized by sizing ventilation equipment correctly, but owners of existing buildings can also control the speed of fans with variable frequency drives.
Many installations with oversized fans use air dampers to regulate flow, often leading to excessive pressure and whistling sounds. In addition, this represents a waste of energy. Reduced speed operation consumes less energy and produces less noise than restricting airflow from an oversized fan running at full speed.
For air ducts in new constructions, avoid 90° turns whenever possible, since these tend to cause turbulence and noise. When air ducts are required to change direction, a better option is to use curved turns or consecutive 45° turns, instead of a sudden 90° angle.
Upgrading Equipment to Improve Efficiency and Reduce Vibration
Equipment is more prone to vibration as it ages, and in many cases it makes sense to consider a new unit. This is especially true if the existing equipment also consumes a lot of energy. For example, modern chillers with variable speed compressors may achieve savings over 50% when they replace old units.
If you are planning to replace the motors on fans and pumps, consider high-efficiency units with speed control:
- For fractional horsepower applications, consider electronically commutated motors (ECMs), also known as brushless motors. They are highly efficient and come with built-in speed control.
- For higher horsepower applications, consider NEMA Premium Efficiency motors equipped with variable frequency drives. Consider that many types of VFDs can run three-phase motors with a single-phase input, so there is no reason to limit your options to single-phase motors.
Vibration and noise can be addressed through prevention or mitigation. In projects that are still in the design phase, it is important to make sure that machinery is properly sized and specified with adequate supports. Also keep in mind that some degree of vibration is normal, so make sure you don’t place machinery rooms close to sensitive areas. Ideally, mechanical rooms should be isolated by hallways, service areas, storage rooms, or other types of rooms that are not occupied permanently.
In existing buildings, vibration and noise issues can be controlled with effective maintenance. Equipment that generates vibration can be mounted on springs or damping pads, and speed control can be deployed for pumps and blowers. If a piece of equipment is very old and producing a lot of vibration, consider a replacement to also improve energy efficiency.